Field of the Disclosure The present application claims the benefit of Korean Patent Application No. 10-2015-0132579 filed on Sep. 18, 2015, Korean Patent Application No. 10-2014-0143576 filed on Oct. 22, 2014, and Korean Patent Application No. 10-2014-0143579 filed on Oct. 22, 2014 with the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entirety.
The present disclosure relates to a slot coater, and more particularly, to a slot coater configured to control a discharge flow rate of a coating fluid for uniform coating.
Description of the Related Art
Generally, a secondary battery includes a battery case and an electrode assembly accommodated in the battery case together with an electrolyte.
The electrode assembly has a structure in which positive electrodes, separators and negative electrodes are stacked alternately. The positive electrode and the negative electrode of the electrode assembly respectively include current collectors made of aluminum foil (Al-foil) and copper foil (Cu-foil). The positive electrode current collector and the negative electrode current collector are respectively coated with a positive electrode active material and a negative electrode active material, and an electrode tab is connected to a portion thereof where an active material is not coated.
For uniform charging or discharging of the secondary battery, a positive electrode active material layer and a negative electrode active material layer should be accurately coated on the current collector. For this, a slot coating using a slot coater is generally performed.
FIG. 1 schematically shows an essential configuration of a general slot coater for performing slot coating. As shown in FIG. 1 the slot coater includes a feeding unit 10 for introducing an active material coating solution, a manifold 11 having a substantially semi-cylindrical shape to accommodate a coating material supplied through the feeding unit 10, a slit 12 communicating with the manifold 11 to discharge the coating fluid, and a die lip 13 where the slit 12 is formed.
The coating solution flows into the manifold 11 through the feeding unit 10 to fill the manifold 11 and discharges out through the slit 12.
The coating solution discharged from the slit 12 is coated onto a substrate which is continuously progressing. A coating width of the active material coated onto the substrate is determined by the width of the slit 12 which corresponds to the length of the manifold 11.
In relation to the slot coater, Patent Literature 1 discloses an interior design method of a slot coating die for continuous uniform forming of an electrode coating catalyst slurry, which includes the step of selecting a fluid model for analyzing flow characteristics of a fluid in a die from variable property information of a catalyst slurry fluid, determining a chamber form in a slot coating die in consideration of the variable properties of the catalyst slurry fluid, and determining a process condition for forming a catalyst layer with a uniform thickness.
In Patent Literature 1, considering a flow rate relationship where a flow rate is fast at a central portion in the width direction of the die and a flow rate is slow at both end portions, the chamber is designed to have a semi-cylindrical shape of a hanger type with a convex central portion so that the coating solution has a uniform speed distribution in the width direction.
However, if a flow rate deviation is improved by changing the shape of the chamber as above, when a coating width is greatly increased to enhance productivity, the slot die may have an excessively great volume to design the chamber to have a hanger-type shape.
Patent Literature 2 discloses an apparatus and method for precise coating, which is configured to discharge a coating solution in an optimal state by installing lips with various shapes to be exchanged with each other. In Patent Literature 2, the precise coating apparatus includes a fixed block, an upstream die and a downstream die respectively installed at an upstream die block and a downstream die block mounted to the fixed block, an upstream lip and a downstream lip respectively fixed to the upstream die and the downstream die in an exchangeable way, and a manifold for supplying a coating solution.
Meanwhile, there has proposed a technique for implementing various coating widths by changing a designed size value of a shim plate which defines the inner space of the manifold and the width of the slit. In other words, as shown in FIG. 2, a manifold 11 having a long length and broad shim plates 14a, 14b, 14c having a size similar to the manifold are adopted to correspond to a coating width in order to increase a coating area, and a non-coating portion 15 is provided at each area between the shim plates 14a, 14b, 14c so that discharge units 16a, 16b, 16c are separated by the non-coating portion 15 in the slot coater.
However, in the slot coater configured as above, a feeding unit 10′ having a pipe shape is connected to the center of the manifold 11 so that a fluid passing through the center has a relatively fast flow rate. For this reason, flow rates at the discharge units 16a, 16b, 16c corresponding to the shim plates 14a, 14b, 14c separated by the non-coating portions 15 are different from each other (see the graph of FIG. 3), and thus different amounts of fluid are coated by the discharge units 16a, 16b, 16c, which deteriorates the uniformity of final products. Therefore, there is needed an urgent improvement.